This invention relates generally to valves and more particularly to poppet valves which have an internal restrictor which is externally adjustable independently of the operation of the poppet to provide variable rates of fluid flow through the valve when the poppet is fully open.
One application of this type of valve is in sootblowers used for boiler cleaning. Sootblowers used a moving jet of air, water, or most often, steam under high pressure from a moving lance to dislodge combustion deposits from the boiler tubes. As the lance is moved in and out of the various access openings in the boiler, it is necessary that the control valve for the steam supply be able to open and close relatively quickly, yet have a flow adjustment that can be readily made during operation.
It has been found that because of the erosive nature of steam on the valve materials, particularly at a flow restriction needed for such an adjustment, it is desirable to provide the adjustable restriction at a point downstream from the poppet valve. The poppet valve can then be operated on a open and closed basis with a fixed length of travel of the poppet to minimize any erosion at the valve seat and ensure a long life for the poppet and especially the valve seat which is relatively expensive to replace and such replacement may require extensive down time. By using a restrictor member that is separate from the poppet and its sealing function, the restrictor member, where the necessary pressure drop takes place, can be replaced or serviced without removal of the valve seat.
One early valve design particularly adapted for sootblowers is shown in U.S. Pat. No. 3,164,364, granted Jan. 5, 1965. This valve has a poppet actuated by a valve stem which in turn is slidable in a valve guide mounted in the valve body. A valve seat is mounted in the lower portion of the valve body to seal with a valve poppet connected to the end of the stem. Above the valve seat is a restrictor surface which cooperates with another restrictor member threadably engaged on the valve guide and prevented from turning by a pin threaded into the side of the valve body. To adjust the valve, it is necessary to remove the pin and insert a tool to rotate the restrictor member, and therefore, this member is not adjustable while the valve is in operation.
An improvement over the above valve is shown in U.S. Pat. No. 5,135,198, granted Aug. 4, 1992. The layout of this valve is generally similar to the one described above, but in this case, the restrictor member also fits over the valve stem with an engagement between non-circular surfaces. As a result, it is possible with this arrangement to rotate the valve stem, and hence, the restrictor member so that it can move on the threads of the valve guide to and from the restrictor portion of the valve seat. However, the restrictor member can be replaced for servicing only by completely disassembling the valve including removing the valve guide, since the valve seat assembly is welded in place. Thus, while this design allows adjustment of the restrictor without removing the valve from the sootblower, it still does not allow easy replacement of any of the component parts.